$borderData:top right bottom left;
@mixin box($name,$size,$where,$color) {
	.#{$name}{
		@each $var in $borderData {
			@if $where == $var {
				border-#{$var}:$size solid $color;
				
			}@else{
				border-#{$var}:$size solid transparent;
			}
		}
	}
}
.box{
	overflow: hidden;
}
.box>div{
	float: left;
}

@include box(num1, 20px, top, red)
@include box(num2, 30px, bottom, pink)
@include box(num3, 40px, left, blue)
@include box(num4, 50px, right, yellow)